Calycosin suppresses expression of pro-inflammatory cytokines via the activation of p62/Nrf2-linked heme oxygenase 1 in rheumatoid arthritis synovial fibroblasts

Abstract The activation of synovial fibroblasts (SFs) and the subsequent production and expression of pro-inflammatory cytokines play a crucial role in the pathogenesis and progression of rheumatoid arthritis (RA). In the current study, rheumatoid arthritis synovial fibroblasts (RASFs) isolated from the joint of the patients were used to evaluate the suppressive effects of calycosin (CAL), a compound derived from the Chinese medicinal herb Radix Astragali , on the expression of pro-inflammatory cytokines in RASFs. The results demonstrated that increased mRNA expression levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-25 (IL-25), interleukin-33(IL-33) were significantly inhibited by CAL. Furthermore, the compound obviously suppressed IL-6 and IL-33 secretion. The key inflammatory mediator, cyclooxygenase-2 (COX-2) was significantly attenuated by CAL. A mechanistic study showed that the antioxidant enzymes heme oxygenase-1 (HO-1), NAD(P)H dehydrogenase quinone 1(NQO1) and Nrf2 of RASFs were markedly activated by CAL. Furthermore, CAL potentiated the accumulation of sequestosome 1 (SQSTM1, p62) and the degradation of Kelch-like ECH-associated protein 1 (Keap1), thereby inducing Nrf2 translocation from the cytoplasm to the nucleus. Thus, CAL suppresses the expression of pro-inflammatory cytokines via p62/Nrf2-linked HO-1 induction in RASFs, which suggests that the compound should be further investigated as a candidate anti-inflammatory and anti-arthritic agent.